The correct order of atomic or ionic size

Options

A. N `lt`Li `lt`B
B. Cl `lt` Mg `lt` Ca
C. `Ca^(2+)ltS^(-2)ltCl^(-)`
D. `Na^(+)ltMg^(+2)ltCl^(-)`

Answer

To determine the correct order of atomic or ionic size, we need to consider several key principles regarding atomic structure and ionic charge. Here’s a step-by-step solution:

### Step 1: Understand the Trends in Atomic and Ionic Size
- **Atomic Size Trend**: Atomic size decreases from left to right across a period due to increasing nuclear charge, which pulls electrons closer to the nucleus. Conversely, atomic size increases down a group because additional electron shells are added.
- **Ionic Size Trend**: For ions, the size depends on the charge:
- Anions (negatively charged ions) are larger than their neutral atoms because the addition of electrons increases electron-electron repulsion.
- Cations (positively charged ions) are smaller than their neutral atoms because the removal of electrons reduces electron-electron repulsion and allows the remaining electrons to be pulled closer to the nucleus.

### Step 2: Compare Atomic Sizes
- Compare elements in the same period:
- For example, Lithium (Li) is larger than Boron (B) because Li is to the left of B in the same period.
- Compare elements in the same group:
- Calcium (Ca) is larger than Magnesium (Mg) because Ca is below Mg in the same group.

### Step 3: Compare Ionic Sizes
- For ions, compare the charge:
- Sulfide ion (S²⁻) is larger than Chloride ion (Cl⁻) because S²⁻ has more electrons, leading to greater electron-electron repulsion.
- Magnesium ion (Mg²⁺) is smaller than Sodium ion (Na⁺) because Mg²⁺ has a higher positive charge, pulling its electrons closer to the nucleus.

### Step 4: Establish the Correct Order
Based on the above trends, we can establish the following order of sizes:
1. **For neutral atoms**: Li > B (Lithium is larger than Boron)
2. **For ionic sizes**: S²⁻ > Cl⁻ (Sulfide is larger than Chloride) and Mg²⁺ < Na⁺ (Magnesium is smaller than Sodium)

### Conclusion
The correct order of atomic or ionic size can be summarized as:
- **Li > B > Mg < Ca** (for neutral atoms)
- **S²⁻ > Cl⁻ > Na⁺ > Mg²⁺** (for ions)

### Final Answer
The correct order of atomic or ionic size is:
- **S²⁻ > Cl⁻ > Na⁺ > Mg²⁺ > Ca > Mg > B > Li**